Some extra security measures include bomb-detection dogs, security cameras and uniformed officers. Event chairwoman Sharon Korn said there will be other safety measures that won't be so easily noticed.

Korn said the April 15 Boston bombings that killed three and injured hundreds led organizers to take a harder look at race security.

St. Louis Police Chief Sam Dotson also urges participants to report anyone who looks suspicious. He said while there are no plans to search every bag, people should carry clear backpacks if possible.